1. Field of the Invention
This invention relates to filter tubes and specifically to filtering devices and filter tubes used for pressure filters employing diatomacious earth, known as bump filters.
2. Description of the Prior Art
Filter tubes utilizing earth coatings over a braided tube have met with a large degree of success in the filter industry especially for high volume fine filtering. Normally, the filter tube consists of an outer braided portion or sheet supported by an inner spring which gives the tube its shape and body. The end of the tube sheet intended to be mounted, usually has a collar device to which the outer sheet or skin of the outer filter tube is sealed and the end is closed. The opposite end of the tube sheet is closed either in the standard tube by sealing the ends or in the recyclable tube by means of a screw fastening that engages with the spring. The inside of the filter tube confines the spring which holds the skin relatively stationary during normal operations. This will enable a coating of filtering particles to build up on the outside of the tube to act to produce the filtering effect.
Examples of such prior art filters are found in U.S. Pat. Nos. 3,100,190; 3,642,141; 4,872,981; 5,230,131 and 5,407,570 to Hobson which are incorporated herein by reference.
Additional examples of prior art filters and related apparatus are shown in the following patents.
U.S. Pat. No. 2,480,320 to Carrier discloses filtering apparatus supporting a plurality of filter elements at the upper and lower ends. A spring and motor at the upper end provide oscillations for removal of sludge. The upper supporting end is removable to permit removal and replacement of filters.
U.S. Pat. No. 2,570,132 to Koupal concerns apparatus for cleaning filter elements of the air-bump wash types. Loss of air is avoided by provision of a solid wall in the inlet chamber as a more suitable air storage space. The need for airtight seals is eliminated and previous impervious upper portions of the filter elements are omitted and the full length of the filters can be used with shorter elements.
U.S. Pat. No. 2,934,209 to Franck describes a fluid dehydrator with improved filtering. The fluid to be dehydrated is passed through a shell filled with a desiccant which can be contaminated by oil in the fluid. A strainer is employed at the inlet to strain out particulate material before passing through the desiccant. A second filter at the outlet provides further filtering of the fluid passing into a second desiccant chamber.
U.S. Pat. No. 4,094,784 to Hirano discloses apparatus for filtering, dehydrating and drying suspension material. A filter mesh is supported on a rotatable valve plate in a vertical cylinder. The mesh collects a cake which is dried, vibrated and dropped through a lower opening by tilting the plate.
U.S. Pat. Nos. 4,422,938 to Miller and 4,427,547 to Miller concern a backwashing filter apparatus which utilizes an inner tapered housing to provide an annular outer flow passage that decreases from inlet to outlet. This provides a uniform liquid velocity through the filter in both forward and back flow operation. A grid support for the inner filter is formed of a plurality of ring-like segments stacked end to end.
U.S. Pat. No. 4,552,661 to Morgan describes a liquid filter device having replaceable self-retaining filtering bags which are formed to snap fit into a groove within the upper portion of the filter housing.
It has been noted that these earth filtering type of apparatus have various phases to the filtering cycle, one phase of which requires back flushing and shaking or bumping to remove the existing contaminated filtering coat and the other to then reapply the coat. During this time, it is possible for particles of dirt in the system to pass through the skin of the filter tube. Not all of these particles may pass from the filter tube beyond the tube sheet and be expelled prior to the succeeding filtering operation. Instead they may settle to the bottom of the filtering tube where they can remain until an inopportune time arises during the normal filtering cycle and then these particles will pass into the filtrate producing a contamination and a less than optimum result of the filtering process.
Heretofore in the past it has been difficult if not impossible to remove these entrapped particles of dirt from the filter and stream because they are usually at the end of the tube where the velocity stream is the lowest and there is the least agitation. The greatest velocity of particles passing through a tube will usually occur at the point near the tube support sheet.